Method of flame working materials



Oct. 12, 1965 J. A. BROWNING 3,211,242

METHOD OF FLAME WORKING MATERIALS Filed July 23, 1963 6 Sheets-Sheet l INVENTOR.

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METHOD OF FLAME WORKING MATERIALS Filed July 23, 1963 6 Sheets-Sheet 2 INVENTOR.

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United States Patent 3,211,242 METHOD OF FLAME WORKING MATERTALS James A. Browning, Hanover, N.H., assignor to H. E. Fletcher Co., West (Iheimsford, Mass, a corporation of Massachusetts Filed July 2.3, 1963, Ser. No. 297,097 8 Claims. (Cl. 175-14) The present invention is a continuation-in-part of my co-pending application Serial No. 666,680, filed June 19, 1957, now Patent No. 3,103,251.

This invention relates to various types of flame working including flame cutting, flame channelling, flame drilling flame surfacing and flame removal of naturally occurring mineral materials such as granite, taconite and other substances.

Flame working, in its broadest aspect, may be thought of as proceeding in two ways, one by means of an open flame having negligible momentum, the other by means of a jet flame characterized by relatively high momentum. The open flame is typified by such devices as the Wellknown oxy-acetylene torch. Such flames, due in large part of their negligible momentum characteristics, are not satisfactory for flame Working mineral bodies for the reason that it is necessary to generate a certain minimum momentum in order to complete the separation of mineral particles from the mineral body. Open flames cannot be made effective by increasing their velocities because these velocities must be limited to a value less than that which results in flame extinction.

In a jet flame of relatively high momentum characteristics, with which the present invention is concerned, the stream of products of combustion is caused to issue from a confined space in which combustion has taken place. In other words, combustion occurs under superatmospheric pressure after which the jet flame issues from an orifice at very high velocity. This jet flame velocity, which is directly correlated with the pressure existing in the combustion chamber, furnishes high momentum characteristies to the flowing mass.

In flame working mineral bodies such as granite, taconite, and other such heat spallable minerals as now commonly practiced, it has been a general assumption in the art that most efflcient flame working is realized when utilizing jet flames of high velocity, temperature and momentum characteristics. For example, velocities in excess of 3400 f.p.s. in the range of 4500 F. such as may be produced by oil and oxygen burned in enclosed flame chambers.

In the course of development work directed towards testing the validity of these general assumptions, it has been observed that they are incorrect. In certain mineral working conditions, reduction of flame velocity and momentum results in more eflicient progress of the work. In other cases, a substantial reduction in temperature may result in a spectacular and totally unexpected increase in removal rate of spalled material. In fact, certain minerals which, as a practical matter, cannot be spalled by the conventional high temperature oxy-fuel flame, are readily spalled by a flame jet whose temperature is well below even that of a stoichiometric air-fuel flame.

I have discovered that these phenomena may be explained by the particular temperature gradient induced in the worked surface of the mineral body, which gradient is affected by temperature of the flame jet and also by its velocity. The two together cooperate to produce a heat flux which establishes and maintains a particular gradient as spalling progresses. I have also discovered that an optimum thermal gradient is one which results in spalling of particles of substantial size and avoids fusion of any of the mineral components.

3,211,242 Patented Get. 12, 1965 From a recognition of temperature gradient control possible in a mineral body, there has been conceived the idea of selectively controlling the momentum and temperature characteristics of a jet flame of the oxy-fuel type and applying the jet flame to a mineral body in such a way as to provide an adequate temperature and a regulated velocity and momentum which is chosen with reference to the mineral working conditions encountered.

I have further discovered that temperature gradient control and superior flame working of a mineral body may be carried out by the introduction of an inert gas into the flow of reactants to a flame, and by controlling flame velocity and momentum characteristics while producing the flame in an enclosed flame chamber. Thereafter, the products of combustion may be released through an oriflce at velocities always above those of an open flame and moreover controlled so as to match the characteristics of the mineral body.

In this invention superior flame working of a mineral body is carried out by a jet flame whose temperature range is substantially attenuated by the presence of inert gas which also provides mass to contribute to the momentum of the jet. The invention flame is thus characterized by having more momentum and lower temperature in relationship to total heat released than conventional jet mineral working flames, or conversely by having less total heat release and lower temperature in relation to momentum.

The jet flame may be produced according to the best form of the invention by causing combustion to take place at superatmospheric pressure in a confined chamber, in the presence of an inert gas along with fuel and an oxidant such as oxygen. The inert gas and the stream of products of combustion of the burned fuel are thereafter directed into contact with the surface of a mineral body.

The preferred oxidant is oxygen and the preferred inert gas is nitrogen. The proportion of nitrogen and oxygen may be as in atmospheric air. Some enrichment of air with oxygen may be desirable for certain materials, or for certain others dilution of the jet with an excess of air beyond that required for fuel combustion may be desirable. In the case of oxygen enrichment of air a higher temperature than that of an air-fuel flame may be produced; in the case of excess of air a lower temperature is produced than the temperature which results from combustion of fuel and air in stoichiometric ratio. Matching temperatures thus controlled to the particular minerals being worked is hereinafter discussed in greater detail. Gases other than those found in air may be used and the same results obtained by controlling the proportion of the inert gas to the oxidant.

I have discovered that the rate of removal with some minerals is increased greatly if a considerable amount of inert gas is supplied with the oxygen. In the case of one particular granite, for example, the maximum rate of removal is found to occur with 50% oxygen and 50% nitrogen. With air, even though not enriched, removal efliciencies comparable to those obtainable with pure oxygen may be obtained. I also find that this increased rate of removal is accomplished by significant increase in the particle size of mineral particles which are removed by spalling.

Since the cost of the removal process is to a considerable extent dictated by the cost of the oxygen, it is also desirabie to consider the process from the standpoint of amount of material removed per cubic foot of oxygen. On this basis the 50% oxygen mixture is far more efficient than the pure oxygen and even un-enriched air is better than pure oxygen.

The principal reason for the benefits obtained by producing a flame and applying it to a mineral surface in accordance with the invention is that no excess of thermal or velocity energy is applied, which excess would cause undesired fusion of the mineral body or unnecessary reduction of size of spalls removed from the mineral body.

The present invention not only reduces the cost of spalling operations, as well as providing improved removal rates, but also diminishes the hazards and nuisance of conventional jet operation. A smaller portion of the mineral is reduced to respirable dust particles, and the noise is dimished to a tolerable intensity.

The nature of the invention and its other objects and novel features will be more clearly understood from the detailed description of the figures of the invention, in which:

FIGURE 1 is a diagrammatic View showing in perspective a greatly enlarged section of a granite body wherein constituent particles have been represented as being joined together along irregular planes of joinder and at the upper side of this mineral body there is further indicated a flame cutting tool arranged to remove particles in accordance with the method of the invention;

FIGURE 2 is another diagrammatic view indicating schematically a typical flame tool supporting apparatus for holding the flame tool in one desired working position in relation to a granite body;

FIGURE 3 is a detailed fragmentary view of the cutting tool shown in FIGURE 2 and indicating more specifically the area along which material may be removed in a channelling operation;

FIGURE 4 is a detailed view of the cutting tool of the invention shown in the operation of drilling a hole in a body of granite;

FIGURE 5 is another detail view illustrating diagrammatically the step of applying a flame cutting tool to a body of granite to carry out a surfacing operation;

FIGURE 6 is a graph indicating results obtained in cutting granite at various heat fluxes;

FIGURE 7 is a cross-sectional view showing details of a flame cutting tool of the invention;

FIGURE 8 is a view in cross section of a novel burner apparatus for carrying out secondary fuel burning;

FIGURE 9 is a diagrammatic view illustrating a burner with secondary fuel addition and indicating the flame components impinging against a surface of spallable material;

FIGURE 10 is a graph illustrating a curve of removal rate of spallable material carried out by means of the secondary fuel;

FIGURE 11 is another graph illustrating curves comparing regions of stable combustion with percentages of fuel required for maximum rates of removal of spallable material;

FIGURE 12 is a cross sectional view of a modified form of burner of the invention.

The invention is in general based on the novel concept of inducing a controlled thermal gradient in a spallable mineral body, employing an oxy-fuel jet flame whose spalling characteristic or capability is tailored or matched to the mineral body by utilizing appreciable quantities of an inert gas so as to desirably attenuate the temperature of the jet flame as it moves into contact with the mineral body.

Referring more in detail to the method and structures shown in the figures described, attention is directed to FIGURE 1, in particular, wherein numeral 2 denotes the flame cutting apparatus of the invention which is shown in a suspended position such that a flame jet 4 is caused to impinge against a surface of the mineral body of granite or granite-like composition and induce a thermal gradient therein. The mineral body is made up of a multiplicity of mineral particles as 40, 5, 6, '7, 8, 9, etc. These particles are joined together in a manner characteristic of granites and granite-like materials along continuous planes of joinder which have been indicated diagrammatically in FIGURE 1 and denoted by numerals as 10, 11, 12, 13, 14, etc.

In accordance with the invention, I modify the conventional oxygen-fuel type flame jet to obtain the flame d of the invention and I apply this modified flame jet 4 in a selective manner to induce thermal stresses in the mineral body shown in FIGURE 1, for example, so that there is produced differential expansion in the particles 3, 4a, 5, 6, 7, 3, and 9, and separation of these particles is caused to take place along some of the planes of joinder noted at the numerals 10, 11, 12, 13 and 14 without the individual particles being subjected to degradation either by way of disintegration or by fusing.

The preferred form of tool comprises the apparatus shown in FIGURE 7 and comprises a tubular body 7a which defines the combustion chamber 6a. Air supplied for combustion enters the burner through tube Ia. In this case No. 2 fuel oil is metered into the stream of air to form a combustible mixture. The oil is introduced through the metering orifice 3a from the tube 2a. Orifice 3a is designed to allow optimum fuel flow at the delivery pressure used. Tube 1a is supported to the combustor 7a by means of shoulder 4a and collar 5a.

The mixture of air and fuel enters the combustion chamber 6a. Ignition is obtained by allowing only a small flow of fuel and air to issue unburned from the nozzle exit 8a. With flows adjusted correctly an auxiliary flame, or spark, causes these fluids to ignite beyond the exit 8a. The flame then flashbacks into the combustion chamber 6a. The air and fuel flows are then turned up to their desired values to form a flame jet of attenuated temperature values as compared with the conventional jet burner.

For the low combustion chamber pressures used (3-12 p.si. gauge) in practicing this invention in one desirable form, it has been found that the chamber wall 7a need not be cooled by means other than radiation. However, it may be desirable to supply additional cooling to wall 7a. One possible method of supplying such cooling effect is to allow the air for combustion to flow at high velocity over wall 7a before introduction to chamber 6a.

Combustion is nearly completed within the chamber 6a and the products produced issue through the nozzle exit 8a. The burner is designed to produce a jet of temperature and velocity characteristics within the range of this invention.

The superior results of the present invention are shown by the curves of FIGURE 6 which were obtained as a result of actual tests. In these curves, heat flux is plotted against efficiency. Heat flux is defined as B.t.u.s per square inch of orifice area per hour, and efficiency is defined as cubic inches of mineral removed per cubic foot of oxygen necessary for complete combustion. In each case, the fuel was kerosene.

As recognized by those skilled in the art heat flux is primarily the product of velocity times temperature. Since temperature for any curve on the chart does not change greatly, heat flux can be considered primarily a function of velocity and will increase with an increase in velocity. Velocity of any given flame is, of course, readily computed by means well-known in the art.

The first curve is for oxygen. The conventional jet channeller operates at the indicated point. Along this curve, temperatures range from a maximum of about 5400 F. at low heat flux to about 4500" F. at high heat flux. At the point indicated for conventional jet channelling flames, velocity is well over 4000 feet per second. It will be noted that a peak occurs in the curve at a velocity of about 1200 feet per second which is well below sonic Velocity.

When 50% nitrogen is added to the oxygen, the second curve is obtained along which the temperature is approximately 1000 F. lower. A peak occurs at about 1000 feet per second at which most eflicient operation results. At this point sonic velocity is about 3000 feet per second. There is a third curve which represents air, that is nitrogen and oxygen in approximate proportions of 79 and 21. For this curve the efliciency peak occurs at a jet velocity of about 800 feet pere second, at which point the temperature is about 3000 F. and with a sonic velocity of 2500 feet per second. At this point the efiiciency of removal is greater than that with the pure oxygen.

In comparing the efficiency peak of the air curve with the conventional oxygen jet flame, it will be noted that the temperature is 3000 F. rather than about 4500 F. and that the jet velocity is 800 feet per second as compared with over 4000 feet per second as noted above. The efficiency, which is the volume of mineral removed per unit volume of oxygen, is greater with air than with oxygen. On an economic basis, more effective removal is obtained much more cheaply with air than with oxygen.

For higher rates of removal and for higher efficiencies, the air may be enriched with oxygen to give the 50% oxygen operation as shown by the optimal curve in FIG- URE 6. This has been found to be most effective for certain mineral bodies. For economic reasons, it may be preferable to use pure air because of the cost of the added oxygen.

The curves shown in FIGURE 6 are the results from working with a certain granite. With other minerals different curves would result.

For example, tests were made on a certain slate which proved impenetrable with the conventional oxy-fuel flame. Its high temperature caused fusing which covered the work surface with molten slag and prevented any spalling act-ion.

With a stoichiometric air-fuel flame jet, with its much lower temperature, only slight fusing was caused, and satisfactory spalling action occurred.

It was discovered that fusing could be completely eliminated and spalling action considerably increased by utilizing an even lower flame temperature. This was accomplished by appreciably increasing the flow of inert gas, using additional air as the inert gas. In this particular case an excess of 75% over the stoichiometric flow of air produced the optimum result. It will be noted that the oxygen in the excess air is considered as inert, and has only .a cooling effect. In this case the temperature of the flame Was reduced to less than 2000 F.

In addition to fuels such as propane and kerosene, there may also be employed various petroleum derivatives and other fuels. Similarly, in some instances, it may be desired to use other oxidants.

The superior cutting characteristics of the jet flame of the invention may be advantageously employed in any of the various cutting operations already outlined above and illustrated diagrammatically in FIGURES 25, inelusive. Thus, in FIGURES 2 and 3, I have illustrated a flame tool 20 which is supported in a vertically adjustable carrier 22 in turn received on a supporting structure 24. By means of this arrangement, a channel may be cut in a horizontal direction through a block of stone 21a to carry out desired quarrying operations. Preferably, the tool 20 is started at a bottom point on the granite face and gradually raised as it cuts by the adjustable carrier. In FIGURE 4, a flame tool 30 is shown being employed to drill a round hole and, in FIGURE 5, a flame tool 32 is shown being employed to carry out a surfacing operation of a block of granite 34.

In connection with operations such as channeling and drilling, the method of the invention is found to be surprisingly effective in overcoming a long standing problem arising when cutting a body of granite having a discontinuity such as often occurs in natural rock formations. A discontinuity such as a crack, seam, bed, or the like interferes seriously with conventional flame cutting.

The conventional flame, as it approaches such a discontinuity, is slowed up in its rate of cutting and the immediately adjacent flame worked surface tends to become plastic due to softening and fusion of some of the rock components, and spalling practically ceases. Even where some rock components do not soften, if the general matrix of the stone becomes plastic, an unsoftened particle is unable to set up mechanical stresses against the soft matrix and, therefore, cannot cause the strains necessary to produce spalling. Further progress in the rock in many instances, therefore, will require removal of the burner and the application of mechanical penetration of the discontinuity by conventional tools at increased expense: and loss of time.

However, the flame of this invention overcomes these difficulties. Its much lower temperature reduces the tendency of the minerals adjacent to the discontinuity to soften or fuse, and consequently less difficulty is encountered. In some cases, the flame of this invention will penetrate discontinuities with no difficulties at all and, in any case, it will approach much closer to the discontinuity before any difficulties occur.

I have further discovered that, by carrying out a secondary fuel addition, I am enabled to produce a localized heating whereby heat is distributed over a wider area of contacted mineral surface. I find that, as increasing percentages of secondary fuel are employed, there is arrived at a point at which an abrupt increase in rate of removal of spalled material is observed and a process of substantially increased efliciency is realized. This point is, I find, for one certain granite, represented by a fuel percentage of approximately 20%.

I have further observed that with the addition of secondary fuel the visible jet becomes appreciably larger. Until the total fuel consumed reaches 20% of the mixture, the spalled particles remain relatively small, i.e., less than 1 inch in diameter. Above 20% of the fuel content, the spalling becomes much larger, increasing to several inches in diameter. The thickness of such larger spallings is only slightly greater than for the smaller ones. It is this size change of spalled particles which leads to the dramatic increase in mineral removal rate.

The limits of flammability for a primary fuel of propane air are about 3% fuel on the lean side and 13% on the rich side, as suggested in FIGURE 11. Thus, the only primary fuel mixtures which will burn must have fuel concentrations contained between these two values. As the amount of reactants is increased, the flammability limits draw closer together until a point is reached where no mixture Will burn within the restricted chamber. Other fuels and oxidants exhibit different flammability limits, but, in general, they are all characterized in the same fashion. It is of interest to note that, the peak allowable flow of gases is at a fuel content slightly richer than the stoichiometric value. Although a flame may be stabilized at fuel concentrations greater than 10%, it was found that the burner began to oscillate badly. For practical purposes, therefore, an upper limit of 10% for the propane-air system is used, as noted above.

In accordance with the invention, these limits of flammability for primary fuel may be substantially exceeded by employing the secondary fuel addition apparatus shown in FIGURES 8 and 9. Primary air is introduced to the burner through the tube 101 from an adequate supply of pressurized air. Primary fuel is introduced into this air from a tube 102 through a metering orifice 103. The injector system is contained within the shoulder 104 which, in turn, is attached to the large tube 1105. Tube 105 forms the enclosure 106 which is called the combustion chamber. The mixture issues into this chamber where it is ignited and burned. The expanding products of the combustion issue through the throat 109 to exit at high velocity at 110.

To this point, the usual primary-type of combustion internal burner has been described. In order to add further quantities of fuel without disturbing the stability of primary combustion, additional fuel is added through tube 107 and metered by the orifice contained in 108. The exiting jet now contains the products of combustion of the primary mixture plus the added secondary fuel.

2" This jet has mineral cutting qualities which are considerably more desirable than when the primary jet is used alone.

Until a total fuel percentage of about is reached, the mineral removal rate remains essentially linear with increased fuel content. As shown in FIGURE 10, however, beyond about 20% fuel the removal rate increases very rapidly. It is this greater than linear increase which makes the secondary fuel addition especially suitable for mineral cutting. The graph shows that, in some cases, it may be more desirable to operate a burner with a fuel content of than it is to scale-up a burn-er three-fold using a mixture strength of 10%. In the former case, for the material used, the removal rate would be about 16 inx /ft. of primary oxygen, while, for the burner of triple size, the equivalent fuel consumption would only remove about 12 in. /ft. From an economic standpoint, this is quite significant. The same amount of fuel is made to do more cutting and uses one-third as much compressed arr.

It is pointed out that the temperature of the flame jet is not increased by the presence of the secondary fuel. It is rather an increased area of action which is responsible for the improved rate of cutting, as has been indicated diagrammatically in FIGURE 9. As noted therein, the flame may be thought of as being made of an inner et or core 12% of relatively larger momentum characteristics and a secondary flame body 122 of relatively weaker momentum characteristics but, nevertheless, of a high temperature such as will promote thermal stressing of the mineral surface 124 over a relatively greater area. Thus, it will be seen that there is employed a method of applying heat over a relatively large area to produce larger spalls and periodically sweeping the jet or core of high momentum characteristics into contact with thermally stressed areas to throw off these larger spalls.

When the burner of FIGURES 8 and 9 is operating in the open atmosphere, the secondary fuel burns with ambient atmospheric oxygen which is drawn into the flame et. Although burning with atmospheric oxygen can occur in the open atmosphere and to some extent in the confines of a channel, a somewhat different condition is present in flame drilling holes of appreciable depth. A point is soon reached in cutting a hole where little if any atmospheric oxygen is present and secondary fuel addition hecomes impractical.

For purposes of practicing the invention with a secondary fuel addition in piercing holes of appreciable depth, therefore, I may desire to supply an independent flow of air fuel to the point of flame emission from the burner. This may be done by conducting a stream of air downwardly around the burner in some suitable manner. For example, I may provide a special form of burner construction as shown in FIGURE 12 in which numeral denotes a cylindrical burner structure having a burning chamber 43, a restricted flame outlet 44, and an inlet d1 through which is supplied primary compressed air. Connected into one side of the inlet 41 is a primary f rel conduit 26 which introduces a primary fuel such as kerosene into the primary air as the latter passes into the burner chamber. The fuel is burned in the usual manner at atmospheric pressure to provide a flame jet 48.

In combination with this primary fuel and air burner, I provide a secondary fuel and air enclosure body 54 which is located around the burner in spaced relationship as shown in FIGURE 12. At one end the enclosure body 5% is formed with an inlet 52 concentrically arranged around the inlet 41 to define an annular passageway 54 through which secondary air may be supplied under pressure.

As shown in FIGURE 12, the enclosure body extends down around the burner 42 and is shaped to provide an annular duct 51 which terminates approximately at the paint of emission of the flame 48 from the burner o tl t 4- An oxidant such as compressed air, oxygen enriched air, oxygen, and the like, is led through the annular passageway 54 into a relatively larger annular passageway 56 and becomes mixed with a secondary addition of fuel supplied under pressure through a fuel pipe 53 and fuel injection holes 69.

Secondary addition of fuel and required oxygen for combustion may thus be made at the point of emission of the flame from the burner 42, even though the latter member may be supported in a deep hole as suggested diagrammatically by the broken line 62.

In addition to providing oxygen for combustion of the secondarily added fuel, the flow of compressed gas through the annular passageway 56 provides desirable cooling of the wall of the primary combustion chamber 42 and thereby becomes itself preheated to aid in combusting the secondary fuel. Since the secondary oxidant can be supplied at much lower pressures than the primary oxidant which must maintain the primary chamber 43, at elevated pressure, the equipment to supply secondary oxidant can be quite simple. It is intended that this secondary fuel addition method and apparatus shown and described, may be modified in various Ways and is to be taken as illustrative of other fuel and oxidant supplying arrangements which may be employed, depending on the nature of the work to be done in the mineral body which is being flame worked. For example, it may be desired to supply secondary oxidant so as to provide an outer jet of much higher temperature than the inner jet. Thus there could be carried out heating by a relatively high temperature peripheral jet and scouring by a high momentum central jet of relatively lower temperature.

From the foregoing description of my invention, it will be apparent that I have disclosed an improved method of flame cutting which is characterized by important control features in respect to the efi'iciency and physical aspects of the material removed in certain types of rock cutting operations. I have also devised a unique fiarne producing means which makes use of novel combinations of fuel and oxidants. The novel flame producing means may also be employed in working minerals other than spallable minerals as, for example, frozen earth bodies and other substances.

It is intended that the invention may be embodied in various other forms and modifications, as included within the scope of the appended claims.

Having thus described my invention, what I claim is:

d. In a method of flame working a heat spallable mineral body, the steps which include introducing into a confined chamber a mixture of fuel, oxygen and an inert gas, burning the mixture of fuel and oxygen in the confined chamber at superatmospheric pressure to form a flow of products of combustion, introducing into the flow of products of combustion a second quantity of fuel, releasing the products of combustion with the said second quantity of fuel through a restricted orifice to form a high velocity flame jet in which said second quantity of fuel is combusted, continuously regulating the thermal intensity and momentum of the flame jet with measured amounts of the said inert gas and directing the flame jet and a combusted second quantity of fuel into contact with an exposed surface of said mineral body to induce a thermal gradient of predetermined mineral stressing capability whereby a controlled spalling takes place.

2. A method according to claim 1 in which the said second quantity of fuel is added in an amount which results in the total fuel consumed being in excess of 20% of the mixture supplied to the confined chamber.

3. A method according to claim I in which the second quantity of fuel is supplied in an amount such that the total fuel consumed is in excess of 20% of the mixture combusted and not materially greater than 30% of the mixture.

4. In a method of flame working a heat spallable mineral body, the steps which include introducing into one end of a confined chamber a mixture of fuel, oxygen and inert gas, burning the mixture in the confined chamber at superatmospheric pressure to form a flow of products of combustion, introducing into the flow of products of combustion at an opposite end of the said confined chamber a second quantity of fuel, releasing the products of combustion with the said second quantity of fuel through a restricted orifice to form a high velocity flame jet in which said second quantity of fuel is combusted to produce an extended outer flame region, continuously regulating the thermal intensity and momentum of the flame jet with measured amounts of the said inert gas and directing the flame jet into contact with an exposed surface of said mineral body to induce a thermal gradient of predetermined mineral stressing capability whereby a controlled spalling takes place.

5. A method according to claim 4 in which the second quantity of fuel is introduced into the products of combustion at their point of emission from the confined chamber together with heated air which has passed around the said confined chamber and become mixed with the said second quantity of fuel.

6. In a method of flame working a heat spallable mineral body, the steps which include introducing into one end of a confined chamber a mixture of fuel and oxidant, burning the mixture in the confined chamber at superatmospheric pressure to form a flow of products of combustion, introducing into the flow of products of combustion at an opposite end of the said confined chamber a second quantity of fuel, releasing the products of combustion with the said second quantity of fuel through a restricted orifice to form a high velocity flame jet in which said second quantity of fuel is combusted to produce an inner high velocity core of flame and an outer relatively low velocity region of flame around said high velocity core of flame.

7. In a method of flame working a heat spallable mineral body, the steps which include introducing into one end of a confined chamber a mixture of fuel, oxygen and an inert gas, burning the mixture of fuel and oxidant in the confined chamber at superatmospheric pressure to form a high velocity flow of products of combustion, introducing a second quantity of fuel and air into the high velocity flow of products of combustion at the point of emission from the confined chamber and directing the flame jet into contact with an exposed surface of said mineral body to induce a thermal gradient of predetermined mineral stressing capability whereby a controlled spalling takes place.

8. A method as defined in claim 6 in which the point of flame working is carried out in a relatively deep hole and the second quantity of fuel and air is supplied through conduits extending into said hole to maintain continuous combustion therein.

References Cited by the Examiner UNITED STATES PATENTS 1,379,179 5/21 Good 15828 2,688,843 9/54 Pitt 6035.6 2,689,452 9/54 Jordan 6035.6 2,711,070 6/55 Henning 158-4 2,896,914 7/59 Ryan 175-14 X 3,004,137 10/61 Karlovitz 17516 3,030,769 4/62 Badders 60-356 3,093,197 6/63 Freeman et al 175--14 CHARLES E. OCONNELL, Primary Examiner. 

7. IN A METHOD OF FLAME WORKING A HEAT SPALLABLE MINERAL BODY, THE STEPS WHICH INCLUDE INTRODUCING INTO ONE END OF A CONFINED CHAMBER A MIXTURE OF FUEL, OXYGEN AND AN INERT GAS, BURNING THE MIXTURE OF FUEL AND OXIDANT IN THE CONFINED CHAMBER AT SUPERATMOSPHERIC PRESSURE TO FORM A HIGH VELOCITY FLOW OF PRODUCTS OF COMBUSTION, INTRODUCING A SECOND QUANTITY OF FUEL AND AIR INTO THE HIGH VELOCITY FLOW OF PRODUCTS OF COMBUSTION AT THE POINT OF EMISSION FROM THE CONFINED CHAMBER AND DIRECTING THE FLAME JET INTO CONTACT WITH AN EXPOSED SURFACE OF SAID MINERAL BODY TO INDUCE A THERMAL GRADIENT OF PREDETERMINED MINERAL STRESSING CAPABILITY WHEREBY A CONTROLLED SPALLING TAKES PLACE. 